AWS has unveiled a new intrinsic function for CloudFormation called Fn::GetStackOutput, aimed at simplifying the management of infrastructure across multiple AWS accounts and regions. This function allows users to reference stack outputs directly in their CloudFormation templates and AWS CDK applications, eliminating the need for cumbersome manual steps.
Organizations often adopt multi-account strategies on AWS, which necessitates sharing infrastructure values like VPC IDs and database endpoints across different accounts and regions. Traditionally, this required either exporting/importing values or managing complex manual processes. The introduction of Fn::GetStackOutput addresses these challenges effectively.
How Fn::GetStackOutput Works
The Fn::GetStackOutput function resolves stack output references during deployment, offering two significant advantages over the previous export/import model:
- Direct referencing across accounts and regions without the need for explicit exports.
- Reduction in operational overhead and the risk of configuration drift.
Parameters of Fn::GetStackOutput
This function accepts four parameters, allowing for flexible configurations depending on the specific use case:
- Stack name
- Output key
- Region (optional)
- RoleArn (optional)
Practical Examples
To illustrate its use, consider a scenario where a networking stack creates a VPC:
- If both stacks are in the same region and account, no additional parameters are necessary.
- For stacks in different regions, specify the
Regionparameter to locate the referenced stack. - When referencing stacks across different accounts, the
RoleArnmust point to a role withcloudformation:DescribeStackspermissions.
Comparison with Fn::ImportValue
Users familiar with Fn::ImportValue may wonder about the differences:
- Fn::ImportValue: Best for strong referential integrity within the same account and region.
- Fn::GetStackOutput: Ideal for cross-account or cross-region references, providing greater flexibility.
Using Fn::GetStackOutput in CDK
The AWS CDK now utilizes Fn::GetStackOutput to automatically resolve cross-region and cross-account references without additional configuration. This streamlines the development process and enhances productivity.
Getting Started
To implement Fn::GetStackOutput, users can refer to the CloudFormation Template Reference Guide for detailed documentation. This new capability is available in all AWS regions supporting CloudFormation.
Why it matters: The introduction of Fn::GetStackOutput significantly simplifies the management of multi-account and multi-region infrastructures, reducing the complexity and potential for errors.
